Face gears (Crown gears), which are one kind of gears, are widely used in the field of driving wheels mainly used in spinning reels for fishing in Japan. However, in recent years, usefulness of the face gears has been widely regarded, and the face gears have been developed or used also in the field of gearboxes with orthogonal axes and the field relating to aircrafts.
As methods for machining a face gear, the following three methods can be mainly taken by way of example. Namely, there are: (1) forging or casting by means of a female die tooth profile manufactured by an electrode; (2) gear cutting by means of a shaper cutter (pinion cutter); and (3) machining cutting for directly cutting teeth by means of a machining center, with the aid of a ball end mill and theoretical tooth profile coordinates.
The forging or casting of item (1) is a machining method suited for mass production, but an achievable precision differs depending on a precision and a manufacturing technique of a male die electrode for manufacturing the female die. In order to improve a meshing precision, a pair of gears have to be sometimes lapped after being forged.
The gear cutting by means of a shaper cutter of item (2) is not often utilized at present, because its machining efficiency is unsatisfactory, a tooth flank modification is difficult, only few suitable machines (shaper machines) are present, manufacture and management of a tool (helical pinion cutter) are difficult, and so on.
The machining cutting of the item (3) can manufacture a tooth profile whose tooth flank has been modified, so that a high transmission precision can be obtained. However, since it takes a long time for machining, the machining cutting is not suited for mass production.